Hello colleage,
I am working in patch antennas fed by coaxial cable. I use Ansoft HFSS as simulation software. The solution for such a problem given by HFSS is to use Driven Terminal solution type and wave port excitation.
I attempted to use Driven Modal solution type and I got a different solution. In fact, if I increase the dimensions of the air box the radiation parameters change and as the dimensions of the box increase further the changes are greater.
The question is: why this happens?. Why I do not get the same or similar solution as the one using Driven Terminal. In fact, Driven Terminal has to perform a modal conversion to get the fields and if I use Driven Modal this conversion is not necessary, this is why I think that use Driven Modal could be a straighter solution. Actually, what we do to compute the far field parameters of the antenna is to perform a modal analysis of the fields.
Thanks in advance
I understand your problem, and I must say, driven modal is better than driven terminal. Driven terminal is used, for the modal S-matrix solution computed is expressed in
terms of the incident and reflected powers of the waveguide modes. This description does not lend itself to problems where several different quasitransverse electromagnetic (TEM) modes can propagate simultaneously. For structures like coupled transmission lines or connectors, which support multiple, quasi-TEM modes of propagation, it is often desirable to compute the Terminal S-Parameters.
So, basically, we define these two different solver as,
Driven Modal Solution
S-parameters
Y-parameters
Z-parameters
VSWR
Gamma (complex propagation constant)
Port Zo
Driven Terminal Solution
S-parameters
Y-parameters
Z-parameters
VSWR
Power (at port)
Voltage Transform matrix (T)
Terminal Port Zo
Thanks,
I understand your problem, and I must say, driven modal is better than driven terminal. Driven terminal is used, for the modal S-matrix solution computed is expressed in
terms of the incident and reflected powers of the waveguide modes. This description does not lend itself to problems where several different quasitransverse electromagnetic (TEM) modes can propagate simultaneously. For structures like coupled transmission lines or connectors, which support multiple, quasi-TEM modes of propagation, it is often desirable to compute the Terminal S-Parameters.
So, basically, we define these two different solver as,
Driven Modal Solution
S-parameters
Y-parameters
Z-parameters
VSWR
Gamma (complex propagation constant)
Port Zo
Driven Terminal Solution
S-parameters
Y-parameters
Z-parameters
VSWR
Power (at port)
Voltage Transform matrix (T)
Terminal Port Zo
Thanks,
Hi,
For driven model, walls of the air box should be at least quarter wavelength away from the outer most edge of your model (consider all edges if your model is Asymmetric). And this quarter wavelength should be calculated at the lowest frequency of sweep.
Regards
Hi,
First of all, thanks for the answers. However, I have to made some clarifications.
Smrity Dwivedi when you said that "Driven terminal is used, for the modal S-matrix solution computed is expressed in terms of the incident and reflected powers of the waveguide modes" you refer to Driven Modal instead, doesn't it?. Driven terminal is the one that expresses the S-matrix in terms of terminal voltage and currents. The question here is why it is better to use driven Terminal for structures that can propagate multiple quasi-TEM modes. This is because in the driven modal case you are defining the mode directly?
Irfan Shahid: Yes, I left at least lambda/4 the problem is that when I increase the box further the results change.
Kind regards and thanks again for your time
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